This invention relates generally to an electronic switch for use in a television receiver, and particularly relates to an electronic switch in a battery-powered portable television receiver for either manual or automatic turn-on and turn-off operation.
The use of batteries in providing operating voltages for portable television receivers is extensive and on the increase with the increasing popularity of even smaller sized television receivers. Generally, portable television receivers employ rechargeable batteries which may be recharged during periods of non-use and exhibit long operating lifetimes. However, the high voltage requirements of even a small television receiver and the demands imposed upon a mobile piece of electronics equipment as sophiscated as a television receiver have placed strict operating requirements on the portable power supply.
Primary design objectives in this area include providing a system in which power demands on the portable power supply are reduced during operating periods and eliminated when the television receiver is turned off. Prior art systems have employed either mechanical or electronic switches. The former are generally large in size and difficult to integrate into the small confines of the portable television receiver while the latter, while physically small, suffer from current leakage when the television receiver is off. This is a particularly important consideration in the case of a lead-acid electrolytic battery for such storage devices are characterized by a minimum charge level, discharge below which renders the battery unrechargeable and in need of replacement. Another design objective in portable television receivers is the reduction in size of the AC-DC and on-off switches and associated circuitry. Prior art mechanical-type switches have become a more burdensome design consideration as portable television receiver size has diminished and features available therein have increased in number and sophistication.
One approach to reducing the power drain on a storage battery when the energized device does not require power is disclosed in U.S. Pat. No. 3,787,757 to Sheng. Therein is disclosed a high impedence control circuit which draws very little current while maintaining a regulator circuit inactive when the load circuit requires no external power. This circuit is designed for use with an electronic device requiring a periodic, load duty cycle operating voltage such as in a time piece. While capable of substantially reducing battery drain during inactive periods, this circuit, as stated in the specification, continues to draw an infinitesimal quiescent current used to inactivate a regulator circuit connected to the load. This quiescent current, of course, reduces energizing battery lifetime.
The prior art discloses numerous attempts to reduce power consumption in a portable television receiver. One such approach is disclosed in U.S. Pat. No. 3,878,326 to Fitzgerald wherein is discribed a television receiver capable of operating on either an alternating current line voltage or a direct current voltage supply in which power demands on the direct current supply are reduced thus prolonging portable battery lifetime. This is accomplished by a switching scheme in which a portion of the power supply is disabled during DC operation resulting in a reduction in losses in the secondary windings of the horizonal output transformer caused by current flow through the resistance of the secondary windings. Another approach to prolonging battery life in a portable television receiver is disclosed in U.S. Pat. No. 3,767,967 to Luz wherein is discribed a system which provides an instant-on feature for AC and DC operation while allegedly reducing current drain to extend battery lifetime. This is accomplished by removing kinescope filament heating in the "OFF" state of the television receiver. While both of these approaches are directed toward reducing power consumption during television receiver operation, neither is intended nor capable of reducing battery drain when the television receiver is "OFF".
Finally, U.S. Pat. No. 4,005,344 to Gaind et al. discloses a protection circuit for a storage battery energizing a television receiver which decouples the battery from the load when battery discharge drops below a predetermined level. Thus, by monitoring the battery potential and comparing that potential with a predetermined voltage level, the storage battery is protected against load circuit faults and discharge below its minimum safe charge level for the battery. This circuit also is intended to prevent excessive battery discharge while extending battery lifetime during television receiver operation.
The present invention, however, provides protection against the discharge of a storage battery energizing a portable television receiver by completely eliminating battery discharge while the television receiver is off. The present electronic switch also offers small size and an efficient means for controlling the audio output or the entire television receiver either manually or automatically.